The present invention relates to layered structures suitable for thin-film transistors (TFT), and the like, electron devices such as TFT that uses such a layered structure, fabrication method thereof, electron device arrays and display apparatuses.
A flat panel display apparatus such as a liquid crystal display (LCD) panel, plasma display panel (PDP), organic electro-luminescence (EL) device, and the like, generally includes a part formed by patterning a thin film layer, as in the case of active devices such as an MIM (metal-insulator-metal) device or TFT or a light-emitting device.
Meanwhile, a device that uses an organic material for a part thereof or for the entire part thereof draws attention these days particularly in view of its advantageous feature of low cost production and easiness of producing a large area device and further in view of possibility of various functions not achieved by conventional inorganic materials. For example, Patent Reference 1 noted below proposes a field effect transistor that changes carrier mobility thereof in response to an external physical stimulus such as light or heat by using an organic semiconductor material.
Generally, patterning of a thin film layer has been conducted by a photolithographic process. A typical example thereof may be conducted as follows.
(1) Apply a photoresist on a substrate carrying a thin film layer (resist application process).
(2) Remove solvent by applying heat (prebaking process).
(3) Irradiate the photoresist with ultraviolet light via a hard mask patterned by a laser beam or electron beam according to pattern data (exposure process).
(4) Remove the resist at the exposed part by using an alkaline solution (developing process).
(5) Cure the resist at the unexposed part (pattern part) by applying heat (post baking process).
(6) Remove the thin film for the part not covered with the resist film by immersing the substrate in an etchant or exposing the same to an etching gas (etching process).
(7) Remove the resist by an alkaline solution or oxygen radicals (resist removal process).
An active device is obtained after conducting such processes. (1)-(7) for each of the thin film layers forming the device repeatedly. On the other hand, it will be noted that the complexity of the process, which requires also expensive facilities, has increased the cost of the active devices thus produced.
On the other hand, attempts have been made on pattern formation by a printing process in the purpose of reducing the fabrication cost of active devices. For example, Patent Reference 2 describes a method of using an intaglio offset printing process in place of photolithography at the time of patterning a thin film layer constituting a TFT.
FIG. 13 shows this conventional method.
Referring to FIG. 13, a resist 102 is transferred to a transfer roller 103 by rotating the transfer roller 103 over a plate 101 that carries a number of depressions holding therein the resist 102, and a resist pattern is formed on a thin film 105 formed on a substrate 104 by printing the resist 102 by way of the transfer roller 103.
Further, according to Non-Patent Reference 1, there is disclosed a method of forming a metal wiring pattern having a width of about 50 μm with a pitch of about 400 μm by an ink-jet printing process that uses a nano-particle ink.
Non-Patent Reference 2 discloses a method of forming electrode patterns 111, 112 and 113 in a TFT by an ink-jet process as shown in FIG. 14, wherein it should be noted that the entire layers of the TFT are formed of organic material layers. In FIG. 14, it should be noted that the electrode layer 110 forms a gate electrode, the electrode layer 111 forms a source electrode and the electrode layer 112 forms a drain electrode. In the example of FIG. 14, it should be noted that a rib 113 of hydrophobic material (polyimide) is provided on a glass substrate 114 so that there is secured an electrode gap (channel) of 5-10 μm between the source and drain electrodes 111 and 112. The TFT further includes an organic semiconductor layer 115 and a polymer insulator layer 116.
Further, according to Patent Reference 3, there is disclosed a method of forming a conductive film pattern as shown in FIGS. 15A and 15B in which a pattern 121a showing affinity to a liquid and a pattern 121b showing repellence to the liquid are formed on a substrate 121 carrying an organic molecular film by decomposing and removing a part of the organic molecular film 122 on the substrate selectively by the steps of: using an ultraviolet radiation; selectively applying a liquid 123 containing conductive fine particles to the pattern 121a; and further conducting a thermal annealing process.
According to this conventional process, the patterns 121a and 121b of different nature are formed simply by applying ultraviolet radiation to the organic molecular film 122 via a photomask. Thereby, the process of forming the semiconductor device is substantially simplified.
Patent Reference 1
Japanese Laid-Open Patent Application 7-86600
Patent Reference 2
Japanese Laid-Open Patent Application 2002-268585
Patent Reference 3
Japanese Laid-Open Patent Application 2002-268585
Non-Patent Reference 1
SOCIETY FOR INFORMATION DISPLAY 2002 INTERNATIONAL SYMPOSIUM DIGEST OF TECHNICAL PAPER•VolumeXXXIII, p. 753˜755
Non-Patent Reference 2
SOCIETY FOR INFORMATION DISPLAY 2002 INTERNATIONAL SYMPOSIUM DIGEST OF TECHNICAL PAPER•VolumeXXXIII, p. 1017˜1019, Science 290, p. 2123˜2126(2000)